Mobile networks are currently evolving from pure circuit switched (CS) networks towards packet switched (PS) networks, in particular Internet Protocol (IP) based networks, and by that integrate into IP based infrastructures that are also used for the Internet, the World Wide Web, and the datacom industry.
More specifically, technologies allowing voice communication over an IP based network have been introduced. Examples of such technologies are Voice over IP (VoIP) via Digital Subscriber Line (DSL) access or Voice over IP via Wireless Local Area Network (WLAN) access. Also in some mobile networks, technologies which allow voice communication over an IP based network are available. Examples of such mobile networks are mobile networks as specified by the 3rd Generation Partnership Project (3GPP). For example, a mobile network implement an IP Multimedia Subsystem (IMS) as specified in 3GPP Technical Specification (TS) 23.228 V12.0.0 and offer voice communication as an IMS service.
Further, a concept referred to as IMS Centralized Services (ICS) has been introduced which allow for utilizing IMS services over various types of access networks, including not only PS access networks, but also CS access networks. The ICS concept is for example specified in 3GPP TS 23.292 V12.1.0. Using the ICS concept, the IMS voice services may be available via various kinds of radio access technology (RAT), such as Global Systems for Mobile Communications (GSM), Wideband Code Division Multiplex (WCDMA), General Packet Radio Service (GPRS), Enhanced Data Rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), Universal Mobile Telecommunications System (UMTS), and High Speed Packet Access (HSPA). Voice communication with a user equipment (UE) which is connected to the mobile network via a CS access network may then be routed through the IMS.
For scenarios where IMS services are usable by a UE both via PS access networks and via CS access networks, a mechanism referred to as Terminating Access Domain Selection (T-ADS) was introduced to select between multiple possible access types for terminating a call to a UE. The T-ADS mechanism is for example specified in 3GPP TS 23.401 V12.0.0, 23.060 V12.0.0, and 23.292 V12.0.0. According to these specifications, T-ADS may be implemented by a Service Centralization and Continuity Application Server (SCC AS) as for example specified in 3GPP TS 23.237 V12.2.0. The T-ADS functionality of the SCC AS may apply various criteria for selecting between a CS access network or PS access network for terminating an incoming voice session. For example, the SCC AS may obtain capabilities of the most recently used PS access network, e.g., in the form of an “IMS voice over PS session supported indication” and current RAT type, from a subscriber database referred to as Home Subscriber Server (HSS). A corresponding is also described in WO 2011/000672 A1.
If a PS access network is selected for termination and the termination fails, e.g., because it was not possible to allocate sufficient radio resources, then the SCC AS may decide to rather terminate the voice session over a CS access network, i.e., to use Circuit Switched Fallback (CSFB). However, CSFB is not possible in all for a PS access networks, e.g., because no corresponding CS infrastructure is available for certain PS access networks. Accordingly, also termination over CSFB may fail. Such multiple failures of termination may cause a significant delay until the party initiating the call is finally informed that the call cannot be established. Further, such multiple failures also consume precious network resources.
Accordingly, there is a need for techniques which allow for efficiently controlling voice communication of a UE in a mobile network.